Over the years considerable work has been devoted to developing additives for controlling (preventing or reducing) deposit formation in the fuel injection systems of spark-ignition internal combustion engines in particular. In particular, additives that can effectively control fuel injector deposits, intake valve deposits and combustion chamber deposits represent the focal point of considerable research activities in the field. Despite these efforts, further improvements and advances are needed to combat the deposit formation problem as will become more apparent from the following discussion.
In combustion engines using fuel injection systems, those systems operate by forcing fuel into an incoming stream of air. Computer-controlled injection systems measure engine operating conditions such as intake air volume, engine temperature, load and speed, and the make up of exhaust gas. The precise amount of fuel is then injected into the engine. There are several fuel injection systems, including throttle body and sequential multiport injection (MPI). In the throttle body systems, multiple cylinders share an injector. Sequential multiport injection (MPI) systems are more precise and efficient. Currently, they are the commonly used fuel injection system.
In a sequential multi-port injection system, a fuel injector is mounted in the cylinder head or the intake manifold immediately outside each cylinder and its associated intake valve. Each cylinder has its own dedicated fuel injector, which opens independently of the others and it is timed with the opening of the intake valve of the associated cylinder. A fuel pump feeds fuel from the gas tank to the fuel injection system where each fuel injector injects the fuel into the intake manifold of an associated cylinder. Each injector delivers a fuel/air mix prescribed by the power-train control module (PCM) at the right moment. The injected fuel/air mix first passes through an intake valve in an open position and then into the combustion chamber. In MPI's, the fuel/air mix is introduced into the cylinder in the form of a fine mist ready for combustion.
The above-described conventional port-fuel injection (PFI) engines form a homogeneous pre-mixture of gasoline and air by injecting gasoline into the intake port. By comparison, direct injection gasoline (DIG) engines inject gasoline directly into the combustion chamber, like a diesel engine. In this manner, it becomes possible in DIG engines to form a stratified fuel mixture, which contains greater than the stoichiometric amount of fuel in the neighborhood of the spark plug while being highly lean in the remainder of the combustion chamber. Due to the formation of such a stratified fuel mixture, combustion with the overall highly lean mixture can be achieved, leading to an improvement in fuel consumption over that of PFI engines, and approaching that of diesel engines. In DIG engines, like diesel engines, only air is introduced through the intake valve and not a fuel/air mixture like a PFI or MPI engine. However, unlike a diesel engine, spark plugs can be used to ignite the fuel. The fuel is often sprayed directly into the cylinders using a fuel injector. In more recent designs of DIG engines, the injector is often placed in the combustion chamber between the air intake and the exhaust valves.
However, both PFI and DIG engines have been subject to undesired fuel-related deposit problems, especially with respect to the injectors, the intake valves, and in the combustion chamber. In MPI systems, the intake valve may have some contact with a potential deposit-reducing detergent or other additive dispersed in the fuel/air mixture that passes through the intake valve. Nonetheless, these MPI engines experience intake valve deposit (IVD) build up, which ultimately can impair engine cleanliness and engine performance. DIG engines can have even greater IVD problems. In DIG systems in particular, the directly injected fuel does not get any opportunity to contact the intake valves before being introduced into the combustion chamber, so inclusion of a detergent in the fuel will be ineffectual to reduce deposits on the intake valve. Therefore, in these more recent implementations of DIG engine technology in particular, intake valve deposits can not be easily or adequately controlled from the fuel side. There is, therefore, a need for other strategies that might address the engine intake valve deposit problems outlined above.
Lubricating oils used in the internal combustion engines of automobiles or trucks are subjected to a demanding environment during use. Different types of additives have been added to such motor oils in efforts to enhance their performance. For instance, various molybdenum compounds have been used and proposed as performance-enhancing additives for lubricant compositions used as motor oils. There are numerous examples in the patent literature, which describe the use of molybdenum additives variously as antioxidants, deposit control additives, anti-wear additives and friction modifiers, in lubricant compositions. A partial list of such patent references includes, for example, U.S. Pat. Nos. 4,164,473, 5,840,672, 6,103,674, 6,174,842, and U.S. Reissued Pat. No. RE37,363E, among others.
U.S. Pat. No. 5,445,749 describes a method for lubricating metal-ceramic interfaces in hybrid engines by supplying a composition to the interface comprising a carrier fluid and a thiocarbamate, such as molybdenum dithiocarbamates. The carrier fluid is described as being a lubricating oil supplied from a sump, or alternatively a liquid fuel. U.S. Pat. No. 5,445,749 includes examples of compositions prepared of molybdenum dithiocarbamates in liquid fuel as the carrier fluid, and base oil and diluent oil are the only other indicated ingredients of those lubricated fuel compositions.
The addition of molybdenum compounds together with or without a metal-containing detergent to crankcase lubrication oils also has been described in the patent literature. U.S. Pat. No. 6,300,291 describes a lubricating oil composition for use in an engine crankcase to improve low temperature anti-wear performance and fuel economy containing an oil of lubricating viscosity, at least one calcium detergent providing calcium in an amount of 0.058 to 0.58 wt %, at least one soluble molybdenum compound providing Mo in amount of up to 350 ppm Mo, at least one nitrogen containing friction modifier, and at least one zinc dihydrocarbyldithiophosphate compound providing phosphorous in amount of about 0.1 wt %, where the composition has a NOACK volatility of about 15.5 wt % or less.
European Patent EP 0 874 040 B1 describes synergistic organomolybdenum antiwear compositions consisting of (a) an organomolybdenum complex prepared by reacting about 1 mole fatty oil, 1.0 to 2.5 moles diethanolamine and a molybdenum source sufficient to yield 0.1 to 12.0 percent of molybdenum based on the weight of the complex, and (b) an organic sulfur compound selected from the group consisting of 1,3,4-thiadiazole compounds of a specified formula. EP 0 874 040 B1 also describes lubricating compositions containing 0.1 to 10.0 percent by weight of the antiwear composition in combination with a major portion of oil of lubricating viscosity.
U.S. Pat. No. 6,528,463 describes a molybdenum complex for use in crankcase oil that is effective variously to improve oxidative stability and fuel economy, and reduce deposits and wear, in an internal combustion engine. The deposits that may be reduced are represented as being piston deposits, ring land deposits, crown land deposits and top land deposits.
U.S. Pat. Nos. 6,509,303 and 6,528,461 also describe organic soluble molybdenum complex additives and lubricating motor oils containing them.
A need remains for strategies that might reduce the occurrence of intake valve deposits in internal combustion engines.